This invention relates to automatic electric controls for outdoor lighting. In particular, it provides an outdoor lighting control circuit having improvements regarding input operating voltage and electrical power consumption.
Outdoor lighting control circuits have widespread uses to control lamps for illuminating streets, parks, parking lots, and the like. The control circuits typically turn the lamps on at dusk and off at sunrise. It is desired, for reasons of public safety and for economy, that outdoor lighting controls operate reliably for extended periods of time, measured in years.
Another objective is that a single manufactured outdoor lighting control device can provide such long-term reliable operation with a relatively wide range of input operating voltages. The achievement of this variable input operating voltage performance enables the same control device to be used in different locations that have different operating or supply voltages.
Typically, outdoor lighting control circuits include a photosensitive element that responds to the presence or absence of ambient light. The photosensitive element is connected to a relay having contacts that selectively apply operating current to a lamp. The device is to provide sufficient current in the relay coil for reliable operation when receiving an operating voltage at the low end of the specified operating voltage range. It also is to limit the relay current to prevent relay burnout or other destructive operation when operating with a voltage at the upper end of the specified operating range. Further, the device is to provide multi-year reliable operation with an input voltage anywhere in the operating range. One prior outdoor lighting control circuit of this type for operation with a range of input voltages is marked under the designation 6690 "Dual Volt" lighting control by Fisher Pierce of Weymouth, Mass., U.S.A.
Prior circuits for this control of lamps and similar electrical loads in response to ambient lighting conditions have proven less than optimal, and an object of this invention is to provide an electrical control circuit responsive to ambient light that operates with relatively high reliability over a relatively broad range of input operating voltages.
Another object of the invention is to provide a control circuit in the above character that dissipates relatively little electrical power, with a selected range of input operating voltages.
A further object of the invention is to provide a control circuit that automatically turns an outdoor lamp device on and off, at dusk and dawn respectively, at appropriate levels of ambient light and under a relatively wide range of operating voltages.
Still another object of the invention is to provide a control circuit in the above character that is relatively low in manufacturing costs.
Other objects of the invention will in part be obvious and will in part appear hereinafter.